Answer:
The answer is given below
Step-by-step explanation:
The mean (μ) = 21.2 minutes and the standard deviation σ = 3.5 minutes.
the oil-change facility will perform 45 oil changes between 10 A.M. and 12 P.M, therefore the sample size n = 45
there be a 10% chance of being at or below. From the normal distribution table, The z score corresponding to a probability of 10% (= 0.1) is -1.28.
z = -1.28
To calculate the mean oil-change time, we use the formula:
[tex]z=\frac{x-\mu}{\frac{\sigma}{\sqrt{n} } }\\\\ Substituting \ values:\\-1.28=\frac{x-21.2}{\frac{3.5}{\sqrt{45} } }\\\\x-21.2=-0.6678\\\\x=-0/6678+21.2\\\\x=20.5[/tex]